Sealed boxes are used in a number of different fields of human endeavor to house components so that they are shielded from the surrounding environment. Certain electrical circuits, for example, are often housed in radiofrequency (RF) shielded boxes because either the circuits are adversely affected by ambient radio waves or they generate radio waves that could adversely effect surrounding electronic devices. Some chemical processing equipment, such as gas monitors, are likewise housed in sealed containers. This is because these monitors may include some type of burner and be in an environment with a high concentration of a combustible gas, where such a combustion can be dangerous. Many sealed boxes, and especially almost all RF-shielded boxes, are formed of metal, such as copper alloys or stainless steel.
When a typical box is assembled by the selective folding of a specifically shaped sheet of metal, seams are formed along the lines where the sides of the box meet. These seams form openings, which, for a sealed box, must be closed or else they can function as holes between the space in the box and the surrounding environment. In order to close these seams, the sides of some sealed boxes are provided with tabs that wrap around the outer perimeter of the adjacent sides. A disadvantage of this construction is that the tabs form outwardly extending bulges along the outer surface of the box with which they are associated. Consequently, when a lid is placed over the body of the box, the bulges present an irregular surface that prevents the lid from properly sealing over the box body. Small openings are formed between the body and lid, reducing the sealed integrity of the box. This necessitates having to provide the box and/or the lid with some type of coupling mechanism to reestablish the desired RF- or gas-tight seal around the interface between the two parts of the box.
Other shielded boxes are provided with a double-walled structure in order to close off the openings formed by the interwall seams. This type of box has a set of inner and outer walls that are arranged so that the seams associated with the inner walls are offset from the seams associated with the outer walls. One disadvantage of this type of box is that, with its double-walled construction, it requires almost twice as much material to manufacture as other boxes. Moreover, the double walls of this box appreciably add to its overall weight. This reduces the attractiveness of installing the box on aeronautical and space vehicles and to other devices where an overall goal is to have a fixed weight as low as possible.